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New Scientist Live

Planck shows almost perfect cosmos – plus axis of evil

(Image: ESA-Planck collaboration)

By Jacob Aron

The universe is almost perfect, 80 million years older than we thought, and maybe a little bit evil.

That’s the conclusion of a four-year mission conducted by the European Space Agency’s Planck spacecraft, which has created the highest-resolution map yet of the entire cosmic microwave background (CMB) – the first light to travel across a newly transparent universe about 380,000 years after the big bang.

“It might look like a dirty rugby ball or a piece of modern art, but I can assure you cosmologists would have hacked our computers or given up their children to get a copy of this map,” said George Efstathiou at a press conference at ESA headquarters in Paris, France, this morning.

NASA/European Space Agency; graphic by Adam Becker and Peter Aldhous

Planck’s map greatly improves cosmologists’ understanding of the universe, but it does not solve lingering mysteries over unusual patterns in the CMB. These include a “preferred” direction in the way the temperature of the light varies, dubbed the cosmic “axis of evil”, as well as an inexplicably cold spot that could be evidence for universes beyond our own (see image, top).

Planck has been looking for variations in the temperature of the CMB, which emerged at around 3000 kelvin, but by now has cooled to just a few degrees above absolute zero, on average.

Virtual trip

These variations are thought to have arisen from tiny, quantum fluctuations in the very early universe that were stretched out to massive scales during a brief period of accelerated expansion known as inflation. This occurred only 10-34 seconds after the big bang and seeded the distribution of stars and galaxies we see today. The CMB lets cosmologists probe this initial stage, taking them on a “virtual trip to the origins of the universe”, said ESA director general Jean Jacques Dordain.

By analysing the statistical properties of the map, cosmologists can compare their best models for inflation with the universe that we can observe today. The high-resolution results from Planck show very strong agreement with cosmological theory. “The overall conclusion is that standard cosmology is an extremely good match to Planck data,” said Efstathiou. “If I were an inflationary theorist I would be extremely happy.”

The pattern of hot and cold variations in the CMB should be randomly distributed – and they are when comparing small patches of the universe. At larger scales, however, Planck reveals that one half of the universe has bigger variations than the other. Planck’s detectors are over 10 times more sensitive and have about 2.5 times the angular resolution of WMAP’s, giving cosmologists a much better look at this alignment. “We can be extremely confident that these anomalies are not caused by galactic emissions and not caused by instrumental effects, because our two instruments see very similar features,” said Efstathiou.

Bruised cosmos

Planck has also confirmed WMAP’s detection of a large unexplained cold spot in the CMB, which some cosmologists took as a sign that there are universes beyond our own. One model of inflation, called eternal inflation, suggests that new universes are continually popping into existence and expanding. This expansion could cause another universe to collide with ours, creating a “bruise” that would show up as a cold spot in the sky.

These anomalies are sure to be debated for many years to come now that cosmologists have a new source of data. Planck scientists have already used their measurements to refine the speed at which the universe is expanding, described by a parameter called the Hubble constant. The new value means that a galaxy roughly 1 million light years away is moving away from us at 20.59 kilometres per second – less than the current value. The result in turn puts the age of the universe at around 13.82 billion years, roughly 80 million years older than previously thought.

Planck’s results also adjust the relative proportions of ordinary matter and the mysterious dark matter and dark energy thought to make up the bulk of the cosmos – the universe has slightly more matter and dark matter and slightly less dark energy than we thought (see graph). “There is less stuff that we don’t understand, by a tiny amount,” said Efstathiou.

Hawking graffiti

One observation that will leave many particle physicists disappointed is the lack of any evidence for a fourth variety of neutrino. We know there are three kinds of these ghostly particles, which barely interact with ordinary matter – the electron, muon and tau neutrinos. Measurements from WMAP allowed for the existence of either three or four types of neutrinos, but Planck’s more detailed data places the number firmly in the three camp.

The spacecraft’s revelations aren’t over yet though. Today’s results are based on the first 15½ months of Planck’s scans, and there is a similar amount of data to follow in the future. ESA has also yet to release information about the polarisation of the CMB, which will provide an additional view of the cosmic pattern. “To paraphrase Arnold Schwarzanegger, we’ll be back,” said Efstathiou.